Effect of moisture on stabilization of polyacrylonitrile fibers

Abstract

The method of modification through pre-stabilization stretching in the presence of plasticizers, such as succinic acid [1], boracic acid [2], dimethylformamide [3] and zinc chlorid [4] etc., has been adopted to prepare small-diameter carbon fibers, which contain fewer defects per unit volume. But the method is relatively complicated and at risk of introducing new flaws. To overcome the above drawbacks, the authors have introduced a modification into the stabilization process, and have chosen moisture in air as the plasticizer. The process is easy to control by damping the atmospheric air and facilitated to applied to continuous process. Foremost in importance is that the new species has not been used, which guaranteed the required cleanliness in the process. Experiments were performed on a PAN-based 3000filament batch, and the shrinkage of PAN fibers was monitored by the displacement of weight. Stabilization was carried out between the temperatures of 180– 220 ◦C, air flow of 0.3 m3/h. The stabilized fibers were then introduced into the carbonization furnace. The carbonization furnace was heated in high-purity nitrogen from room temperature to 1000 ◦C at a rate of 5 ◦C/min, and heating ceased when the temperature was reached. Finally the fibers were taken out when cooled down to room temperature. Experimental details have been published elsewhere [5] and the experimental setup was shown in Fig. 1. A special barothermohygrograph was utilized to examine the amount of moisture in damp air. The result from Fig. 2 show that the fibers can be more easily elongated with increasing R.H. in air. The total amount of length elongation was about 0.2% at 40% of R.H. as compared with 0.8% at 80%. This means that